Antenna element damping device



9st. 5, 1965 P. R. JONES ANTENNA ELEMENT DAMPING DEVICE Filed June 12.1961 INVENTOR.

PAUL R. JONES ATTORNEYS United States Patent Iowa Filed June 12, 1961,Ser. No. 116,377 8 Claims. (Cl. 343-720) This invention relates to anantenna structure, and more particularly, to a device for substantiallyeliminating vibration caused by external forces acting on an antennaelement.

Antenna structures are commonly subject to various vibration producingforces, particularly wind forces, that have heretofore greatly shortenedthe life of the conventional antenna structure by causing the antennaelements to snap or break, usually near the crossbar supporting theelement.

Many devices have heretofore been proposed, or utilized in attempting tosolve this vibration problem, but none of these devices have beencompletely successful. While vibration of an antenna element couldconceivably be eliminated by disrupting the vortices, it has been foundthat absorbing the energy of vibration by mechanical damping ispreferable, and accordingly, mechanical damping has been utilized inthis invention to provide a relatively simple and inexpensive means,requiring no deformation or reconstruction of the antenna elementitself, for absorbing the energy transferred to the antenna element bythe vibration producing forces.

It is therefore an object of this invention to provide an improvedantenna structure having simple, yet reliable, means for damping out andsubstantially eliminating vibration in an antenna element due tovibratory forces acting thereon.

It is another object of this invention to provide an antenna structurehaving damping means that may be adjustably secured to the antennaelements without deforming or reconstructing the element.

It is a further object of this invention to provide an improved antennastructure including an antenna element and a readily flexible membersecured to a portion of said antenna element subject to vibratory forceswhereby said flexible member substantially eliminates vibration in saidantenna element.

Still more particularly, it is an object of this invention to provide anantenna structure having a readily flexible damping member attached tothe free end of a cantilever antenna element as an extension thereof,said readily flexible member oscillating out of phase with said antennaelement to thereby absorb the energy transferred to the antenna elementby vibratory forces acting thereon.

With these and other objects in view which will become apparent to oneskilled in the art as the description proceeds, this invention residesin the novel construction, combination and arrangement of partssubstantially as hereinafter described and more particularly defined bythe appended claims, it being understood that such changes in theprecise embodiments of the herein disclosed in vention may be submittedas come within the scope of the claims.

The accompanying drawing illustrates two complete examples of theembodiments of the invention constructed according to the best mode sofar devised for the practical application of the principles thereof, andin which:

FIGURE 1 is a perspective view of an antenna structure constructedaccording to this invention;

FIGURE 2 is a side view showing the free end portion of a cantileverantenna element with the damping means of this invention attachedthereto;

3,210,765 Patented Oct. 5, 1965 FIGURE 3 is a cross-section view takenthrough the line 33 of FIGURE 2;

FIGURE 4 is a side view of a second embodiment of this invention withthe damping means shown in section for illustrative purposes; and

FIGURE 5 is a side view of another embodiment of this inventionillustrating the use of the damping means and a corona shield.

Referring now to the drawings in which like numerals have been used forlike characters throughout, the numeral 6 refers generally to an antennastructure having an upright mast 8, usually of relatively largecross-section,

and a crossarm, or boom, 9 to which a plurality of antenna elements 10may be attached. Crossbar 9, which, like mast 8 is usually tubular andof relatively large crosssection, may be attached to mast 8 in anyconventional manner such as, for example, by clamp 12. In addition,antenna elements 10 may likewise be attached to boom 9 in anyconventional manner, such as, for example, by clamps 13. Antennaelements 10 are preferably tubular and of relatively small diameter,and, as shown in FIG- URE 1, may be connected to crossbar 9 so that eachelement has a free or unmounted end portion 14. The antenna elements aretherefore readily susceptible to vibration due to external vibratoryforces, principally wind forces, that frequently cause vibration of theelements which soon causes them to break. However, by addition of lossymembers 16 to the end of each antenna element, as taught by thisinvention, this deficiency in antenna structures may be overcome.

It is to be realized, of course, that two or more of the antennaelements might be connected near their free ends and this would notobviate the need for a damper as taught by this invention since thestructure formed would still be essentially cantilever mounted andtherefore still subject to destructive vibrations.

As shown best in FIGURE 2, lossy member 16, which is preferably ofreadily flexible, electrically nonconductive material such as, forexample, plastic, may be attached to the end of each antenna element bymeans of a conventional fastening means, such as, for example, clamp 18.As shown in FIGURE 3, flexible member 16 is preferably tubular and has adiameter slightly larger than that of antenna element 10 so as to slideover the free end 14 thereof and thereafter be easily maintained inplace by clamp 18, which clamp may be readily adjusted by means of aconventional tightening device 20.

Flexible member 16 acts to absorb the energy transferred to the antennaelement by the vibratory force acting thereon by vibrating, often quiteviolently, as illustrated by the dotted lines in FIGURE 2. Toeffectively accomplish its purpose, the length of the flexible membermust be such that when the antenna element starts to vibrate theflexible member oscillates out of phase with the antenna element to dampout vibration in the element. For maximum effectiveness, the length ofthe flexible member 16 should vibrate with one and one-half modes orthree-fourths standing wave. The antenna element can, of course, beadjusted by moving the damper along the antenna element until the damperis of the proper effective length.

Although shown and described hereinabove as a flexible member of tubularconstruction, it is to be appreciated, of course, that the flexiblemember 16 might be solid and could, for example, fit inside antennaelement 10 and be connected to the free end portion conventionally.

The antenna element may also be reduced in effective length, withoutphysical deformation, by modifying flexible member 16 to provideelectrical end loading. As shown in FIGURE 4, the modified damping orflexible member may include a readily flexible, electricallynonconductive portion 116 of tubular construction surrounding andenclosing a readily flexible, electrically conductive, cylindricalinsert 26 of slightly smaller diameter, which diameter, however, isslightly greater than that of the antenna element. The flexible membermay be attached to the free end 14 of an antenna element in the samemanner as described hereinabove in connection with the first embodimentshown. However, as shown in FIG- URE 4, the electrically conductiveinsert 26 engages free end 14 of antenna element and, by adjusting thepositiouing the flexible member along the end portion 14, the effectivelength of the antenna element may be varied as desired.

In addition, and as shown in FIGURE 5, a disc 30 projecting normallyoutwardly from the antenna element may be provided to serve as a coronashield. Disc 30 is preferably relatively thick and the periphery of thedisc is rounded to avoid sharp edges. As is well known in the art, sucha shield is preferably of electrically conductive material and iselectrically attached to the antenna element at its end portion by anyconventional means, and may be formed as an integral part of clamp 118,as shown in FIGURE 5, since the damper 16 is of electricallynonconductive material.

From the foregoing, it will be appreciated by those skilled in the artthat the improved antenna structure of this invention provides arelatively simple, yet reliable, means for eliminating undesirablevibration in antenna elements.

What is claimed as my invention is:

1'. In an antenna structure, the combination of: a substantially rigidantenna element a portion of which is subject to vibratory forces; and ahollow readily flexible tube connected to the remote end of said antennaelement subject to vibratory forces, flexing of said flexible membersubstantially eliminating vibration in said antenna element.

2. In an antenna structure, the combination of: a substantially rigidantenna element a portion of which is subject to vibratory forces;damping means including a hollow readily flexible tube and anelectrically conductive member connected to said tube, said electricallyconductive member being constrained to movement with at least oneportion of said tube; and means for connecting'said tube to the portionof said antenna element subject to vibratory forces to substantiallyeliminate vibration in said antenna element.

3. In an antenna structure, the combination of: a substantially rigidcantilever antenna element the free end portion of which is subject tovibratory forces; damping means including a hollow readily flexible tubeand an electrically conductive member connected to and constrained tomovement with said tube; and means for connecting said tube to the freeend portion of said antenna element whereby said damping means absorbsthe energy of vibrations transferred to said antenna element by saidvibratory forces.

4. The combination of claim 3 wherein said electrically conductivemember is flexible and engages said free end portion to electrically endload and thereby determine the overall effective length of said antennaelement.

5. In an antenna structure, the combination of: a substantially rigidantenna element subject to vibratory forces and having a free endportion; a hollow readily flexible tube having a cross sectionsubstantially the same as that of said antenna element; and fasteningmeans for fastening one end of said tube to the free end portion of saidantenna element so that the flexing of said tube substantiallyeliminates vibration in said antenna element.

6. The combination of claim 5 including an electrically conductivemember inside said tubular member engaging said antenna element toelectrically end load the same and thereby determine the eflectiveoverall length of said antenna element.

7. The combination of claim 6 wherein said tube is of plastic materialand said electrically conductive member is of metal.

8. The combination of claim 5 including a corona shield extendingradially from and in electrical contact with the end portion of saidantenna element.

References Cited by the Examiner UNITED STATES PATENTS 1,675,391 7/28Stockbridge 174-42 2,460,401 2/49 Southworth 343-785 2,694,101 11/54Shuhart 174-42 2,714,161 11/55 Featherstun 343904 X FOREIGN PATENTS697,608 11/30 France.

648,938 1/ 51 Great Britain.

748,318 4/56 Great Britain.

HERMAN KARL SAALBACH, Primary Examiner.

GEORGE N. WESTBY, Examiner.

1. IN AN ANTENNA STRUCTURE, THE COMBINATION OF: A SUBSTANTIALLY RIGID ANTENNA ELEMENT A PORTION OF WHICH IS SUBJECT TO VIBRATORY FORCES; AND A HOLLOW READILY FLEXIBLE TUBE CONNECTED TO THE REMOTE END OF SAID ANTENNA ELEMENT SUBJECT TO VIBRATORY FORCES, FLEXING OF SAID FLEXIBLE MEMBER SUBSTANTIALLY ELIMINATING VIBRATION IN SAID ANTENNA ELEMENT. 